Free Tool
Invoice Due Date & Late Fee Calculator
Enter your invoice date, payment terms, and late fee percentage to see the due date, how many days overdue it is, and the total amount owed including any late fee.
| Days overdue (as of the date above) | 0 |
| Invoice amount | $0 |
| Late fee owed | $0 |
| Total due | $0 |
Assumption: the late fee is a one-time flat percentage of the invoice amount, applied once the invoice becomes overdue (not compounding per day or per month). If your contract or local rules specify a different late fee structure — daily interest, monthly compounding, or a statutory rate — use that instead; this tool doesn't know your contract terms or local law.
How do I calculate an invoice due date and late fee?
An invoice due date is just the invoice date plus your payment terms — Net 7, Net 14, Net 30, or Net 60 mean the client has that many days from the invoice date to pay. It sounds simple, but a surprising number of payment disputes start with disagreement over which date the clock actually started on, or basic date-math errors when terms span a month boundary. Doing this calculation the same way every time removes that ambiguity.
"Net 30" doesn't mean 30 business days or "by the end of the month" — it means 30 calendar days from the invoice date, unless your contract explicitly says otherwise. If you invoice on the 20th with Net 14 terms, the due date is the 3rd of the following month, not "two weeks into next month" or some rounder date that feels closer. Getting this precise matters once you start charging late fees, because a due date that's off by a few days changes whether a payment counts as late at all.
Late fees themselves are usually set as a flat percentage of the invoice, applied once the payment is overdue — this calculator uses that model, since it's the most common structure for freelancers and small businesses. But late fee rules vary a lot by jurisdiction and by what your own contract or terms of service actually say: some places cap late fees by law, some require the fee to be disclosed on the original invoice to be enforceable, and some businesses use daily or monthly compounding instead of a one-time flat percentage. This tool doesn't know your contract or your local rules — treat the number here as what a simple one-time percentage would produce, and check your actual terms before invoicing a client for it.
Whether or not you actually charge a late fee, tracking due dates consistently is what makes it possible to follow up on time — most late payments aren't disputes, they're just invoices that slipped through the cracks. A clear, consistent due date is the first thing that needs to be right before any of the rest of your collections process works.
Frequently asked questions
What does 'Net 30' actually mean?
It means payment is due 30 calendar days after the invoice date — not 30 business days, and not 'by the end of next month.' The same logic applies to Net 7, Net 14, and Net 60: count that many calendar days forward from the invoice date to get the due date.
Can I legally charge a late fee?
This depends on your contract terms and your local jurisdiction — some places require late fees to be disclosed upfront in your original invoice or contract to be enforceable, and some cap the maximum percentage you can charge. This calculator does the arithmetic for a flat one-time percentage; it doesn't tell you whether that percentage or structure is legally valid where you operate, so check your contract and, if unsure, a local attorney.
Does the late fee compound the longer an invoice stays unpaid?
Not in this calculator — it applies a one-time flat percentage once the invoice becomes overdue, regardless of how many days overdue it is. If your terms specify daily interest or monthly compounding instead, you'll need to calculate that separately, since it's a different formula.
Why does the calculator ask for an 'as of' date instead of just using today?
So you can check any date — including past dates to see how overdue an invoice was on a specific day, or future dates to project ahead. It defaults to today's date automatically, so most users can ignore it entirely.
Want the full system, not just this one number?
This calculator checks one invoice. The Freelancer Finance Toolkit includes a full invoice tracker that logs every invoice's due date, payment status, and days outstanding automatically, alongside a rate calculator and income/expense tracker — so nothing slips through the cracks.
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